| Embryo implantation is a critical step in the establishment of pregnancy, yet the process differs widely among mammalian species. It is important to understood basic reproductive processes such as implantation in order to develop assisted reproductive technologies for endangered species. Yet, implantation is poorly understood in arctoidean carnivores, a group that includes endangered species such as the black footed ferret (Mustela nigripes) and giant panda (Ailuropoda melanoleuca).; Previous studies suggested that a 60 kilodalton basic protein, produced by the corpus luteum (CL) from days 6–9 of pregnancy and pseudopregnancy, was required for embryo implantation in the domestic ferret (Mustela putorius). In this study, I have isolated that 60 kilodalton protein from pseudopregnant ferret CL and identified it as glucose-6-phosphate isomerase (GPI). GPI is a multifunctional protein that was first characterized as the enzyme that interconverts glucose- and fructose-6-phosphate. It also acts as a motility factor during metastasis, a process analogous to embryo implantation.; Passive immunization of pregnant ferrets against GPI decreased the number of implantation sites in a dose-dependent manner. Treatment of ovariectomized, pregnant ferrets with GPI suggested that, while necessary, GPI is not sufficient to cause implantation. GPI immunostaining was detected in pregnant ferret CL, but not uteri, on days 6 and 9, but not days 3 and 12 of pregnancy. A similar change in GPI gene expression by CL did not occur at this time. Plasma GPI activity did change significantly over days 3–12 of pregnancy and pseudopregnancy, reflecting the change in GPI immunostaining. CL explants secreted GPI into culture media. The amount of secreted GPI increased with increasing stage of pregnancy, whereas intracellular GPI activity remained constant. GPI secretion in vivo was not affected by prolactin treatment alone.; I concluded that GPI is the 60 kilodalton implantation protein. GPI is produced and secreted by ferret CL on days 6–9 of pregnancy in ferrets and is required for embryo implantation. Further study is needed to determine whether prolactin, which is also required for implantation, affects GPI expression by the CL. |
